Laminated film

ABSTRACT

A laminated film which comprises a film substrate, an adhesive undercoat of a carboxylated ethylene copolymer composition prepared by copolymerizing a monomer mixture of an Alpha , Beta -unsaturated carboxylic acid or anhydride and at least one vinylidene monomer of the formula CH2 CXY where X and Y are the same or different and each represents hydrogen, chlorine, a lower alkyl containing 1-6 carbon atoms, acetoxy, or a carboxylic ester group in the presence of an ethylene-vinylacetate copolymer applied to said film substrate, and a top film of a polyolefin or ethylene copolymer applied to said adhesive undercoat.

Kosaka et al.

1*Nov. 25, 1975 LAMINATED FILM Inventors: Yujiro Kosaka; Masaru Uemura;

Tokio Fujiki; Mitsutaka Saito, all of Shin Nanyo, Japan Toyo Soda Manufacturing Co., Ltd., Yamaguchi, Japan Assignee:

Notice: The portion of the term of this patent subsequent to July 31, 1990,

has been disclaimed.

Filed: Oct. 2, 1973 Appl. No.: 402,916

Foreign Application Priority Data Oct. 11,1972 Japan 47-101123 US. Cl 428/463; 156/332; 260/878 R; -260/886; 427/407; 427/409; 427/411; 428/474; 428/483; 428/514; 428/518; 428/910 Int. Cl. C09J 3/14; B32B 27/30 Field of Search 117/76 F, 76 P, 75, 122 H; 156/332; 161/256, 251, 218; 427/407, 409, 411; 428/463, 474, 483, 514, 518, 910

References Cited UNITED STATES PATENTS 11/1965 Adelman 156/332 X 12/1969 Dotson et al. 117/122 l-l 3,663,334 5/1972 Mueller-Tamm et al. 156/332 X 3,669,797 6/1972 Fukazawa et al. 156/332 X 3,671,356 6/1972 Keinanen 156/332 X 3,697,368 10/1972 Bhuta et al. 117/76 F X 3,749,756 7/1973 Kosaka et al. 260/878 R 3,838,079 9/1974 Kosaka et al. 260/27 FOREIGN PATENTS OR APPLICATIONS 946,384 l/l964 United Kingdom 260/878 R Primary Examiner-Ralph Husack Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [57] ABSTRACT A laminated film which comprises a film substrate, an adhesive undercoat of a carboxylated ethylene copolymer composition prepared by copolymerizing a monomer mixture of an a,[3-unsaturated carboxylic acid or anhydride and ,at least one vinylidene monomer of the formula CH =CXY where X and Y are the same or different and each represents hydrogen, chlorine, a lower alkyl containing l-6 carbon atoms, acetoxy, or a carboxylic ester group in the presence of an ethylene-vinylacetate copolymer applied to said film substrate, and a top film of a polyolefin or ethylene copolymer applied to said adhesive undercoat.

7 Claims, No Drawings LAMINATED FILM BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates to a laminated film which is very effective as a packaging material. More particularly, it relates to a laminated film which is prepared by coating a carboxylated ethylene copolymer on a smooth surface of a substrate such as a biaxially stretched polypropylene film, a polyester film aluminum foil, cellophane, or the like, and then laminating a polyolefin or an ethylene copolymer such as an ethylene-vinylacetate copolymer on the substrate over the coated surface.

2. Description of the Prior Art:

In the past packaging films have been made from one polymer. Recent attempts to improve the moisture proofing properties, the fragrance retaining properties and the heat sealing properties of films have been made by laminating polymers to form laminated sheets such as polymer/different polymer, polymer/paper, polymer/aluminum foil, and the like. These laminated films have been used for automatic packaging. Further, laminated polyethylene has been widely used in the packaging field. However, the lamination of a resin such as polyethylene on a smooth surface of substrate such as polypropylene, cellophane, polyester film or aluminum foil has been difficult, although the lamination of a resin on a fibrous surface such as paper which has rough surfaces is easy.

In order to improve the adhesive properties of various resins, resins such as polyethylene have been extruded at relatively high temperatures or a surface of the substrate has been oxidized or polar groups have been substituted on the surface to improve the adhesive strength of the surface. Alternatively, adhesive accelerators with substantial polarity have been coated on film substrates or the polarity of the surfaces of the substrates have been increased to improve the adhesive properties of the laminated polymer by a corona discharge treatment. Other methods of increasing the adhesiveness of materials have included a potassium bichromate/sulfuric acid treatment, a flame treatment or ultraviolet ray treatment.

Recently, cold foods have attained increased commercialization and the automatic packaging of these foods has been increased. This increase has required laminated films which can be heat-sealed at temperatures lower than that of polyethylene films within a short time and at the same time achieve seals having high strength. One attempt to solve the problem has been the development of a laminated ethylene-vinylacetate copolymer which satisfies these requirements. However, ethylene-vinylacetate copolymers have a lower heat stability than polyethylene. Thus, the conditions under which conventional laminates of polyethylene are treated cannot be used, which places limitations on the heat treatment of ethylenevinylacetate copolymers. The temperatures at which ethylene copolymers are laminated are usually required to be 50 100C lower than the temperatures at which polyethylene is treated. Because of the low lamination temperatures required, proper adhesion of the ethylene copolymer to the substrates has been very difficult. Adhesive accelerators such as organotitanium compounds, organoaluminum compounds and isocyanate compounds have not been able to improve the adhesive properties. In particular, no way has been found to laminate ethylene-vinylacetate copolymers on biaxially stretched polypropylene with high strength.

I A need continues to exist, therefore, for a method of improving the adhesive characteristics of laminated polyethylene packaging materials. By the procedure of the invention an adhesive accelerator has been developed which is superior to organotitanium adhesive accelerators for the bonding of polyethylene in laminated films.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide a high strength laminated film wherein a polyolefin or an ethylene copolymer is laminated on a substrate.

Briefly, this object and other objects of the invention as hereinafter will become more readily apparent can be attained by coating 21 carboxylataed ethylene copolymer which is prepared by copolymerizing and 04,5- unsaturated carboxylic acid and/or anhydride and at least one vinylidene monomer of the formula wherein X and Y are the same or different and each represent hydrogen, chlorine, lower alkyl containing 1 6 carbon atoms, acetoxy, or carboxylic ester, in the presence of an ethylene-vinylacetate copolymer. The ethylene-vinylacetate copolymer is applied as an adhesive undercoat to a substrate, and then a polyolefin or an ethylene copolymer is laminated to the undercoated surface to prepare a laminated film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The adhesive accelerator which is used in the laminated film of the invention is a carboxylated ethylene copolymer which is prepared by copolymerizing l 80 parts by weight of a monomeric mixture of an 01,3- unsaturated carboxylic acid or anhydride and a vinylidene monomer in the presence of 99 20 parts by weight of an ethylene-vinylacetate copolymer having a vinylacetate content of 5 wt. percent, preferably 10 40 wt. percent and a melt index of 0.1 500 g/min. at a temperature of from 20-l 50C with a radical initiator. Suitable polymerization techniques for the polymerization reaction include solution, suspension, emulsion, and bulk polymerization. Suitable afiunsaturated carboxylic acids or anhydrides include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, and the like. Suitable vinylidene monomers include ethylene, propylene, isobutene, butene-l, octene-l vinylchloride, vinylacetate, lower alkyl esters of acrylic acid or methacrylic acid, and the like.

The carboxylated ethylene copolymer comprises (1) a graft copolymer wherein the B-unsaturated carboxylic acid and the vinylidene monomer are grafted onto the ethylene-vinylacetate copolymer and (2) a copolymer produced by copolymerizing the monomers. It is preferable to use a carboxylated ethylene copolymer having a melt index of 0.1 500 g/l0 min. and an acid value of l 250 mg KOH/g which shows the degree of .carboxylic acid substituted, in order to accomplish the objectives of the invention. Usually, the ratio of the monomers to the ethylene-vinylacetate copolymer is l-80 99-20 percent by weight, and the ratio of the a,B-unsaturated carboxylic acid or anhydride to said vinylidene monomer is l:0.l-l0. The carboxylated ethylene copolymer adhesive accelerator increases the adhesive properties of the laminate when it is placed between the substrate and the laminated polyolefin or the ethylene copolymer. The undercoating of the adhesive accelerator on the substrate can be accomplished by a solution coating method or a heat melt coating method. When the solution coating method is used, the carboxylated ethylene copolymer is dissolved in a solvent of hexane, heptane, benzene, toluene, xylene, ethyl acetate, ethylenedichloride, propylenedichloride, trichloroethylene, trichloroethane, dioxane, tetrahydrofuran, or the like. A 0.5 percent, preferably 2 5 percent solution is prepared and is coated onto the substrate by a roller coating method as adapted for a direct gravure roll coating method, an offset gravure roll coating method, a clipping method or a bar coating method.

The laminate thickness of the solid components is usually in the range of 0.05 l glm preferably 0.15 0.25 g/m which corresponds to a thickness of 0.05 I.Op,, preferably 0.15 0.25;. The substrate to which the polyolefin or the ethylene copolymer is laminated include any of the conventional substrates such as aluminum foil, biaxially stretched polypropylene film, unstretched polypropylene film, polyester film, polyamide film, polyethylene film cellophane film, polyvinylchloride film, kraft paper, and the like. The laminated film to which the polyolefin or the ethylene copolymer is laminated with high strength can be obtained by coating the adhesive accelerator of the carboxylated ethylene copolymer on any substrate and then binding the polyolefin or ethylene copolymer film to the substrate. The bonding effects of the adhesive accelerator can be improved by a mechanical treatment of the surface of the substrate by a corona discharge treatment, a flame treatment, an ultraviolet rays treatment, or the like, before the substrate is coated with the adhesive accelerator.

The laminate can be formed by applying the polyolefin such as polyethylene, polypropylene, an ethylenevinylacetate copolymer, an ethylene-propylene copolymer or the like, to the coated substrate by an extrusion coating method. The laminate can be formed by heatsealing the polyolefin or the ethylene copolymer film on the surface of the substrate having the adhesive accelerator coating with a hot roller. In order to improve the lamination, it is possible to treat the carboxylated ethylene copolymer coated on the surface of the substrate prior to the lamination with a mechanical treatment such as a corona discharge treatment, a flame treatment, or an ultraviolet ray treatment. Lamination of the ethylene copolymer by extrusion coating is performed at temperatures less than the lamination of polyethylene such as at temperatures of 200 250C. Under low temperature conditions it has normally been difficult to obtain ethylene copolymer laminated films. However, laminated films with high strength and high adhesive strength can be obtained by using a carboxylated ethylene adhesive accelerator.

The carboxylated ethylene copolymer can also be applied as an adhesive accelerator to ethylene copolymers such as, for example, ethylenevinylacetate copolymers (melt index of l g/lO min., preferably 2 l5 g/lO min.), with a vinylacetate content of l wt. percent, preferably 1 20 wt. percent, and also to polyolefins such as, for'example, low density polyethylene (melt index 1 20 g/lO rnin., preferably 2 9 g/l() min.), high density polyethylene (melt index I 20 g/lO rnin., preferably 2 9 g/lO min.) and polypropylene (melt fiow index I 2O g/lO rnin., preferably 2 9 g/lO min.). When polyethylene is laminated with the adhesive accelerator of the invention at relatively low temperatures, laminations with high adhesive strength can be attained. In the preparation of articles such as bags, the heat-sealing properties can be improved, which shows the effectiveness of the adhesive accelerator of the invention.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. In the examples, the term percent designates percent by weight unless otherwise noted.

EXAMPLE I A monomer mixture of vinylchloride, maleic anhydride and acrylic acid was copolymerized in the presence of an ethylene-vinylacetate copolymer (vinylacetate content of 30 wt. percent and a melt index of 30 g/lO min. ASTM Dl238-T) in order to prepare a carboxylated ethylene copolymer composition having a melt index of ll g/lO min. and an acid value of 42 mg KOH/g. By this procedure was prepared a composition containing wt. percent of an ethylene-vinylacetate copolymer component and 2 wt. percent of a vinylchloride component. A 5 percent solution of the resulting copolymer composition in toluene was coated on each substrate to a thickness of 3 to 4p. and dried. An ethylenevinylacetate copolymer (vinylacetate content of 10 wt. percent, and a melt index of9 g/lO min.) was melted and extruded through a T-die at 225C onto the coated substrate in a thickness of 40p. in order to prepare a laminated film. The adhesive strength of the laminated films were measured by a friction pull test of a test piece 15 mm wide with Schoppers Tension Tester. The results are shown in Table I.

TABLE I (coss head speed 300 mm/min. distance between chacks mm.)

The surface of the film was treated with a corona discharge.

The results of the untreated laminated films are shown as reference examples. The results indicate that substantial improvement in the adhesivity of the laminates was achieved with the carboxylated ethylene copolymer adhesive accelerator of the invention.

EXAMPLE 2 A monomer mixture of vinylchloride, maleic anhydride and acrylic acid was copolymerized in the presence of an ethylene-vinylacetate copolymer (vinylacetate content of 30 wt. percent and a melt index of 30 g/lO min.) to prepare a carboxylated ethylene copolymer composition having a melt index of-55 g/ min. and an acid value of 35 mg KOl-l/g. By this procedure was prepared a composition containing 86 wt. percent of an ethylenc-vinylacetate copolymercomponent and 3 wt. percent of a vinylchloride componentuA5 percent solution of the resulting copolymer composition in a 1:1 toluene-trichloroethane solution was coated on a biaxially stretched polypropylene film. A laminated product was prepared. by bonding the ethylene-vinylacetate copolymer to a polypropylene substrate by the procedure of Example 1. The adhes'ivestrength of the laminated film as measured .by a friction pull test was 280. g/lS min. I

EXAMPLE'3 A monomer. mixture of propylene andmaleic anhydride was copolymeri zed in the presence of an'ethylene-vinylacetate copolymer (vinylacetate of 26 wt.

percent and a melt index of 8 g/lO min.) to prepare a,

carboxylated ethylene copolymer composition having a melt index of 4 g/lO min. and an acid value of 28 mg KOH/g. By this procedure was prepared a composition containing 93 wt. percent of an ethylene-vinylacetate copolymer component. A 5 percent solution of the resulting copolymer composition in toluene was coated on a biaxially stretched polypropylene film. To the coated film was bonded an ethylene-vinylacetate copolymer to prepare a laminated film in accordance with the procedure of Example 1. The adhesive strength of the laminated film as measured by a friction pull test was 430 g/] 5 min. When aluminum foil was used as the substrate, the adhesive strength of the laminated film was 600 g/ mm.

EXAMPLE 4 A 5 percent solution of the carboxylated ethylene copolymer composition of Example 1 in a 1:1 toluene 1,1,l-trichloroethane solution was coated on each of the substrates shown in Table ll to a thickness of 3 4 1.. An ethylene-vinylacetate copolymer (vinylacetate content of 16 wt. percent and a melt index of 7.5-g/l0 min.) was melted and extruded through a T-die at 240C. The extruded polymer was bonded to the coated substrates at a thickness of 40p. to prepared a series of laminated films. Also, polyethylene (density of 0.917 g/cc and a melt index of 8 g/lO min.) was melted and extruded through the T-die at 310C. The extruded polyethylene polymer was bonded to the coated substrate at a thickness of 20p. or 40p. to prepare several laminated films. The adhesive strength of the laminated films was measured and compared as shown in Table II.

EVAzethylene-vinylacctale copolymer EXAMPLE 5 A' monomer mixture of ethylacrylate and maleic a'nhydride was cop'olymerized in the presence of an ethylene-vinylace'tatc copo yme r (vinylacetate content of 36 wt. percent a'nda melt index of 30.g/l0 min.) to prep'are a carboxylated ethylene copolymer composition having a melt index of 15 g/lO min. and an acid value of 20 mgKQH/g. By'this procedure was prepared a composition containing 65 wt. percent of the ethylenev'inylace'tate"copolymer component. A 5 percent solution of the resulting copolymer composition in toluene was coated on the substrates shownin Table Into a thickness of3'. Su, and dried. An ethylene-vinylacetate copolymer (vinylacetate content 6 wt. percent and a melt index of 8 g/lO min.) was melted and extruded througha T=die at 270C. The extruded polymer was bonded to the' coated substrates at a thickness of 20p. to prepare a laminated film. Also,"polyethylene (density of 0.917) was melted and extruded through a T-die at 315C onto several coated substrates at a thickness of 20;; to 40;; to prepare a series of laminated films. The adhesive strengths of the laminated films were measured and compared as shown in Table III.

Having now fully described this invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.

What is claimed as new and intended to be covered by letters patent is l. A laminated film which comprises:

a film substrate wherein said film substrate is aluminum foil, biaxially stretched polypropylene film, unstretched polypropylene film, polyester film, polyamide film, polyethylene film, cellophane, polyvinylchloride or kraft paper and wherein said top film is polyethylene, polypropylene, an ethylene-vinylacetate copolymer or an ethylenepropylene copolymer; an adhesive undercoat of a carboxylated ethylene copolymer composition prepared by copolymerizing a monomer mixture of an 01,13- unsaturated carboxylic acid or anhydride and at least one vinylidene monomer of the formula wherein X and Y are the same or different and each represents hydrogen, chlorine, a lower alkyl group containing l 6 carbon atoms, acetoxy, or a carboxylic ester group in the presence of an ethylene-vinylacetate copolymer, wherein the ratio of said monomer mixture to said ethylenevinylacetate copolymer is l-80 99-20 parts by weight and the ratio of said :,[3- unsaturated carboxylic acid or anhydride to said vinylidenc monomer is l 0.l-l0, wherein said ethylenevinylacetatc copolymer contains -70 wt percent of a vinylacetate component and has a melt index of 0.1 500 g/lO min, applied to said film substrate; and a top film of a polyolefin or ethylene copolymer applied to said adhesive undercoat.

2. The laminated film of claim 1, wherein said afiunsaturated carboxylic acid or anhydride is acrylic, methacrylic, maleic, fumaric, itaconic acid or anhydride and said vinylidene monomer is ethylene, propylene, isobutene, butene-l octene-l, vinylchcloride, vinylacetate, lower alkylesters of acrylic acid or methacrylic acid.

3. The laminated film of claim 1, wherein said carboxylated ethylene copolymer composition is applied as an undercoat on said film substrate as a solution pre- 8 pared by dissolving said carboxylated ethylene copolymer composition in a solvent of hexane, heptane, benzene, toluene, xylene, ethyl acetate, ethylenedichloride, propylenedichloride, trichloroethylene, trichloroethane, dioxane or tetrahydrofuran.

4. The laminated film of claim 1, wherein said film film is an ethylene vinylacetate copolymer. 

1. A LAMINATED FILM WHICH COMPRISES: A FILM SUBSTRATE WHEREIN SAID FILM SUBSTRATE IS ALUMINUM FOIL, BIAXIALLY STRETCHED POLYPROPYLENE FILM, UNSTRETCHED POLYPROPYLENE FILM, POLYESTER FILM, POLYAMIDE FILM, POLYETHYLENE FILM, CELLOPHANE, POLYVINYLCHLORIDE OR KRAFT PAPER AND WHEREIN SAID TOP FILM IS POLYETHYLENE, POLYPROPYLENE, AN ETHYLENE-VINYLACETATE COPOLYMER OR AN ETHYLENEPROPYLENE COPOLYMER; AN ADHESIVE UNDERCOAT OF A CARBOXYLATED ETHYLENE COPOLYMER COMPOSITION PREPARED BY COPOLYMERIZING A MONOMER MIXTURE OF AN A,B-UNSATURATED CARBOXYLIC ACID OR ANHYDRIDE AND AT LEAST ONE VINYLIDENE MONOMER OF THE FORMULA
 2. The laminated film of claim 1, wherein said Alpha , Beta -unsaturated carboxylic acid or anhydride is acrylic, methacrylic, maleic, fumaric, itaconic acid or anhydride and said vinylidene monomer is ethylene, propylene, isobutene, butene-1, octene-1, vinylchcloride, vinylacetate, lower alkylesters of acrylic acid or methacrylic acid.
 3. The laminated film of claim 1, wherein said carboxylated ethylene copolymer composition is applied as an undercoat on said film substrate as a solution prepared by dissolving said carboxylated ethylene copolymer composition in a solvent of hexane, heptane, benzene, toluene, xylene, ethyl acetate, ethylenedichloride, propylenedichloride, trichloroethylene, trichloroethane, dioxane or tetrahydrofuran.
 4. The laminated film of claim 1, wherein said film substrate is aluminum foil.
 5. The laminated film of claim 1, wherein said film substrate is biaxially stretched polypropylene film, unstretched polypropylene film or polyethylene film, and wherein said top film is polyethylene film, polypropylene film or an ethylene-propylene copolymer film.
 6. The laminated film of claim 1, wherein said film substrate is polyester film, polyamide film, cellophane, polyvinylchloride or kraft paper.
 7. The laminated film of claim 1, wherein said top film is an ethylene vinylacetate copolymer. 